1. Field of the Invention
The present invention relates generally to a method for producing microcomposite powders and, more particularly, to a method for producing microcomposite powders utilizing a metallorganic solution which itself is formed from an ammonium soap solution.
2. Description of the Prior Art
Presently, the most commonly used methods for producing microcomposite materials, powders or cermets involve mechanically mixing powders of the desired components by ball milling, and thereafter rolling or shaking in either a wet or dry environment. However, it is very difficult to produce a homogeneous sintered product using these methods due in part to differences in size, shape, or density among the various components blended to form the microcomposite materials or powders.
An alternate approach is through the use of microcomposite precursor powders consisting of the desired components or phases. Such powders are capable of producing relatively homogeneous composites using conventional fabrication methods without mechanical mixing. Microcomposite powders consisting of metallic and non-metallic phases have also been produced using mechanical cladding and chemical solution techniques. The chemical techniques include precipitation and sol-gel processes in which salts or gels containing the desired ions are produced. Composite powders can then be made by precipitating the product around the suspended particulate phase.
The precipitates produced from these methods often consist of refractory anions such as halides and sulfides or low melting nitrates. The removal of these refractory anions requires high temperature processing. Fine particles may be difficult to produce from nitrates due to melting and agglomeration or grain growth during processing. In addition, many of the salts contain unwanted cations such as Na.sup.+ or K.sup.+ which may also be difficult to remove.
A method recently developed at the Naval Research Laboratory produces a superconducting composite formed from YBa.sub.2 Cu.sub.3 O.sub.7-x (YBC) and silver (Ag). These YBC/Ag composites use Ag coated powders. This method utilizes a technique involving the dissolution of silver nitrate (AgNO.sub.3) into an appropriate solvent. Superconducting powders are mixed into the solution wetting the surfaces of the powder particles. The solution is evaporated, causing the precipitation of AgNO.sub.3 particulates onto the ceramic surface which are then melted and decomposed to form a metallic Ag coating. Because a continuous coating is formed, it is difficult to produce small discrete particles within the matrix as evidenced by the presence of Ag particles as large as 25 microns present in the samples.
Another technique has been reportedly used recently to make a soluble bismuth compound (bismuth 2-ethylhexanoate) for sol-gel synthesis of Bi-based superconducting compounds. An soluble Bi compound is produced by dissolving Bi(NO.sub.3).sub.3 into an ammonia soap solution. The oily product is extracted with xylene and isolated by removing the solvent under vacuum. However, it is reported that when the product was mixed with other organic solvents in an attempt to produce intimately mixed precursors of the Bi--Ca--Sr--Cu--O superconducting compound, the resultant mixture failed to produce these desired precursors.
As seen from the foregoing, the known methods for producing advanced microcomposite materials or powders for superconducting applications all have unique shortcomings which severely limit their reliability and effectiveness and thus prevent them from being used in industrial and government applications on a regular and competitive basis. Consequently, a need exists for an improved method for producing advanced microcomposite materials or powders for superconducting applications which overcomes the shortcomings of these known methods.